A little lizard that lurks in Costa Rica’s waterways has its very own superpower. It can breathe underwater. Like humans, it has grasped the knack of scuba-diving, but it has no need for regulators or air tanks. All it requires is a little bubble of air attached to its snout.
Reporting her findings in the Natural History Notes of Herpetological Review, Lindsey Swierk of Binghamton University stumbled upon the scuba-ready reptiles by chance. While walking along mountain streams in Costa Rica, she noticed that certain lizards, known as water anoles (Anolis aquaticus), were spending impressively long periods of time submerged underwater.
“Finding evidence suggesting that water anoles ‘breathe’ underwater was serendipitous, and not part of my original research plan,” Swierk said in a statement. “I was impressed and pretty confused about the length of the dive, which gave me an itch to take a closer look with an underwater camera in the next couple of years.”
Impressively, water anoles can remain underwater for up to 16 minutes. We humans can only manage about three minutes, although very accomplished free-divers can hold their breath for about 20.
So how do the lizards do it?
The scaly aquanauts breathe beneath the surface using a small pocket of air attached to their noses. As they breathe out, the air bubble forms, and then they re-inhale it, possibly along with some other little air pockets trapped around their heads.
“I think it’s possible that some additional air pockets are being trapped around the anole’s head and throat, and that the inhalation and exhalation of the air bubble allow for some trading of fresh air among these air pockets, allowing the anole to swap air in its current air bubble with ‘new’ air,” explained Swierk, who is the first to document this breathing behavior in water anoles.
“It’s additionally possible that the air bubble plays a role in allowing an anole to get rid of carbon dioxide. I suspect that there might be morphological adaptations, namely the shape of the top of the anole’s head, which allows a large bubble of air to cling to it easily.”
The reason the anoles stay below the surface is probably to do with predators. If you lack speed, as anoles do, concealing yourself underwater is a pretty good way to hide. Swierk also found evidence of aquatic insects in the lizards’ stomachs, suggesting that their scuba-diving strategy might also allow them to feed underwater.
Swierk now hopes to find out exactly why the incredible behavior has evolved and whether the shape of an anole’s head helps it to maintain its vital air bubble.
“If future investigation reveals that this rebreathing behavior is adaptive, then I would imagine that it is a trait that evolved over time to allow water anoles, and perhaps similar anole species, to thrive in their aquatic habitats,” she said.